There has been well known a blind nut as disclosed, for example, Japanese Utility Model Laid-Open No. 58-186208 (Publication 1, see, particularly, FIG. 2B). The blind nut is formed as a hollow internally threaded tubular body with one end having a flange, using a plastically deformable material such as metal. The tubular portion of the blind nut is inserted into a mounting hole of a workpiece to bring the flange into surface contact with the workpiece and cause buckling in a part of the tubular portion. In this way, the blind nut is fixed to the workpiece while clamping the workpiece between the buckled portion and the flange. The blind nut is conveniently set to a workpiece, such as a large panel, having difficulty in accessing to the backside thereof, because such a setting operation can be performed from one side. A bolt can be screwed into the blind nut fixed to the workpiece to allow an additional component to be attached to the workpiece through the bolt. A press nut has also been known as one of nut-type fasteners other than the blind nut. For example, one press nut is disclosed in Japanese Utility Model Laid-Open No. 63-35809 (Publication 2). Typically, the body of the press nut has one end formed with an insertion portion to be inserted into a mounting hole of a workpiece, and the insertion portion is forcedly inserted into the mounting hole to fix the press nut to the workpiece.
A blind-nut setting apparatus is used in the operation of setting a blind nut to a workpiece. A conventional blind-nut setting apparatus is disclosed, for example, in Japanese Patent Laid-Open Nos. 51-142171 (Publication 3), and 63-52974 (Publication 4: Japanese Patent Publication No. 4-789), Japanese Utility Model Laid-Open No. 1-84842 (Publication 5: Japanese Utility Model Publication No. 3-35464) and Japanese Patent Laid-Open No. 2001-510733 (Publication 6). While these conventional blind-nut setting apparatus are different from each other in their detailed structure, they are commonly constructed by utilizing an air pressure and an oil pressure for intensifying the air pressure. The blind-nut setting apparatus has a basic structure comprising: a nose having a mandrel which is disposed at the front end thereof and formed with an externally thread to be threadedly connected with a blind nut; a hydraulic cylinder for receiving therein a hydraulic piston for axially pulling the mandrel; and a handle portion having an oil reservoir formed therein for containing oil to be supplied to the hydraulic cylinder, and an air cylinder for receiving therein an air piston to allows a ram connected to the air piston to be reciprocatingly advanced and retracted in the oil reservoir. In this structure, upon triggering, compressed air is supplied to the air cylinder to move the air piston to advance the ram in the oil reservoir to thereby supply oil from the oil reservoir to the hydraulic cylinder so that the hydraulic piston is moved to pull the mandrel, whereby the blind nut threadedly connected with the mandrel is set to the workpiece.
The blind-nut setting apparatuses disclosed in the above Patent Publications 3 to 6 are advantageous in that upon triggering after supplying of compressed air from outside, a blind nut threadedly connected with the mandrel is desirably set to a workpiece, such as a panel, at a desired fixing force. In an operation of setting a blind nut to various workpieces different in thickness using the conventional blind-nut setting apparatuses including the above blind-nut setting apparatuses, the pulling length (stroke) of the mandrel is changed according to the variations in thickness. For example, if a workpiece is changed from a thin panel to a thick panel (or multiple panels), the setting operation has been completed by moving the mandrel over a shorter pulling length (stroke), and thus, the mandrel must be adjusted to have a shorter stroke. When such a setting apparatus required for managing a setting force by adjusting the stroke of the mandrel is used to set a blind nut to a workpiece having a non-uniform or large variation in thickness (e.g. FRP: Fiber Reinforced Plastic), an adequate setting force can be obtained only if the stroke of the mandrel is adjusted in compliance with the variation in thickness of the workpiece on a case-by-case basis.